Mix flour and salt for the crust. Add cold butter, then gradually add ice water until the dough forms a ball. Press into a 9-inch pie dish, refrigerate while preparing the filling.
In a saucepan, whisk together sugar, egg yolks, butter, cornstarch, lemon zest, and 2 tablespoons lemon juice. Cook over medium heat, stirring until the mixture thickens and coats a spoon (5-7 minutes). Remove from heat, stir in remaining lemon juice, and cool completely.
In a separate bowl, beat egg whites until stiff peaks form. Gently fold into the cooled curd. Pour into the chilled pie crust, spreading evenly.
Whip heavy cream or coconut milk with vanilla extract until soft peaks form. Fold in cream cheese and sour cream. Spread the cream mixture atop the curd layer.
Chill for 2 hours before slicing. Arrange lemon slices and zest on top before serving.